IK + Pole Target {Rig} is =//= Twisting my Characters Mesh
Turning on Axes for the bones can be really helpful when things twist, and/or before parenting mesh to rig. Like it seems in your case, the twist occurs when you parent mesh to rig with Auto-Weights.

I suspect a complete bone rotation in Y axis in one step, (Y axis is Up for bones)

So probably step 1 can solve it, step 2) 3) are more indepth regarding IK.


What happens if you change IK Solver to iTaSC

Sometimes adding stiffness can solve at least weird rotational behaviour.